Binary bi-phase shift modulator

ABSTRACT

A binary bi-phase shift modulator having an input piezoelectric transducer and an output piezoelectric transducer connected in series between a radio frequency input and a radio frequency output. A fixed DC pole voltage having a first polarity is connected to one of the transducers. A DC switched pole voltage is connected to the other transducer which switches between the pole voltage of the first polarity and a pole voltage of the opposite polarity in accordance with a binary data signal. The polarity of the radio frequency input relative to the radio frequency output varies as a function of the polarity of the DC switched pole voltage.

GOVERNMENT INTEREST

The invention described herein may be manufactured, used, and licensedby or for the United States Government.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates generally to modulators and, moreparticularly, to a bi-phase piezoelectric resonator modulator.

II. Description of Relevant Art

There are many applications for low speed radio frequency modulators atrelatively low frequencies, i.e. less than 100 megahertz. For example,such modulators can be used in conjunction with remote sensors totransmit the sensor data from the location of the sensor and to acentral station. Such modulators are used in many types of sensors suchas troop movement or tank movement sensors, weather condition sensors,and the like.

In these types of sensor applications, as well as other applications,the speed of the modulator is not critical and relatively slow speedtransmissions of data are sufficient for the application. Instead, amuch more critical requirement of such modulators is that the modulatorconsumes as little power as possible. This is particularly true sincethe sensor is often installed at locations lacking electric power. Inthese situations, battery power, or even solar panel power, must besufficient to power the modulator as well as the other associatedequipment. To date, the battery or solar panel requirements necessary topower the modulator and associated equipment are relatively large and/orbulky.

SUMMARY OF THE PRESENT INVENTION

The present invention provides a bi-phase resonator modulator whichovercomes all of the above mentioned disadvantages of the previouslyknown modulators.

In brief, the present invention provides a bi-phase shift modulatorhaving an input piezoelectric transducer and an output piezoelectrictransducer which are connected in series between a radio frequency inputand a radio frequency output. A source of radio frequency, e.g. asinusoidal rye, is coupled to the input transducer. The frequency of theradio frequency signal is relatively low, i.e. less than 100 megahertzand preferably less than 30 megahertz.

A DC pole voltage having a first polarity is connected to one of thetransducers. Blocking, capacitors are also connected in series betweeneach transducer and its associated input or output. Consequently, theblocking capacitors minimize or even eliminate the current draw from thesource of the bias or pole voltage.

A DC switched bias or pole voltage is connected to the other transducerwhich switches between a pole voltage having the same polarity as thefirst transducer, and a pole voltage of the opposite polarity inaccordance with a binary data signal. Thus, the DC switched pole voltagephase modulates the radio frequency signal between a first state inwhich the radio frequency input signal is in phase with the radiofrequency output signal, and a second state in which the phase of theradio frequency input is 180 degrees out of phase from the radio signaloutput. The actual phase of the DC switching pole voltage varies inunison with the binary data signal. Subsequent demodulation of the phasemodulated signal at the base or central station extracts the data fromthe radio frequency signal.

Preferably, the piezoelectric transducers are both lead zirconatetitanate (PZT) acoustic resonators. Furthermore, the piezoelectrictransducers are preferably dimensioned so that their resonant frequencycoincides to the frequency of the radio frequency signal to minimizesignal loss from the radio frequency input and to the radio frequencyoutput. Furthermore, the entire modulator is preferably implemented asan integrated circuit.

BRIEF DESCRIPTION OF THE DRAWING

A better understanding of the present invention will be had uponreference to the following detailed description when read in conjunctionwith the accompanying drawing, wherein like reference characters referto like parts throughout the several views, and in which:

FIG. 1 is a schematic view of a preferred embodiment of the presentinvention;

FIG. 2 is an enlarged vies illustrating an implementation of the presentinvention on an integrated circuit; and

FIGS. 3A-3C are waveforms illustrating the operation of the modulator.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION

With reference first to FIG. 1, a preferred embodiment of a bi-phaseshift modulator 10 according to the present invention is shown. Themodulator 10 includes an input piezoelectric transducer 12 and an outputpiezoelectric transducer 14. The input and output transducers 12 and 14,respectively, are connected in series between a radio frequency input 16and a radio frequency output 18. A blocking capacitor 20 is alsoconnected in series between the transducer 12 and the radio frequencyinput signal 16 and, similarly, a blocking capacitor 22 is connected inseries between the output of the output transducer 14 and the Output 18for the modulator.

The radio frequency signal 16 is preferably a sinusoidal signal of arelatively low frequency, i.e. less than 100 megahertz. Furthermore, thevalue of the blocking capacitors 20 and 22 is selected to block DC, butpass a signal at the frequency of the RE signal 16. For example,assuming a frequency of 19 megahertz for the radio frequency signal 16,a value of about 31 picofarads for each capacitor 20 and 22 issufficient to pass the signal from the radio frequency input 16, throughthe blocking capacitors 20 and 22 and transducers 12 and 14, and to theoutput 18.

The input and output transducers 12 and 14 are preferably piezoelectriclead zirconate titanate (PZT) acoustic resonators. The transducers arealso dimensioned to resonate at substantially the frequency of the radiofrequency signal 16. By matching the resonant frequency of thetransducers 12 and 14 to the frequency of the radio frequency signal 16,signal loss from the radio frequency input 16 and to the radio frequencyoutput 18 is minimized.

A DC voltage source 24 having a first polarity, e.g. +8 volts, isconnected through a resistor 26 to pole or bias the input transducer 12.Since the resistor 26 is connected in between the input transducer 12and the blocking capacitor 20, essentially zero current flows throughthe resistor 26. Consequently, power consumption from the bias or polevoltage source 24 is eliminated, or at least minimized.

A switched DC bias or pole voltage source 28 is electrically connectedthrough a resistor 30 to the output of the output transducer 14 and theblocking capacitor 22. Like the blocking capacitor 20, the blockingcapacitor 22 eliminates or at least minimizes the current flow throughthe resistor 30 and thus minimizes or eliminates the power consumptionfrom the DC switched bias or pole source 28.

The output from the DC switched voltage source 28 is switched inaccordance with data from a data stream between a first value equal tothe poling voltage of the fixed DC voltage 24 of the first polarity anda pole voltage of the same magnitude as the voltage source 24, but ofthe opposite polarity. For example, assuming that the voltage of thefixed DC pole source 24 is 7 volts, the DC switched voltage source 28will switch the pole voltage applied to the output transducer 14 between+7 volts and −7 volts depending upon the digital or binary value of thedata.

With reference now to FIGS. 3A-3C, the net effect of changing thepolarity of the pole voltage on the output transducer 14 is illustrated.More specifically FIG. 3A illustrates a radio frequency sinusoidalsignal 32 at the radio frequency input 16 (FIG. 1). Assuming that thepole voltage applied by the DC switching source 28 to the outputtransducer 14 has the same polarity as the fixed pole voltage source 24,an output signal 34 at the output 18 is in phase with the input signal32 as shown in FIG. 3B. Consequently, the phase of the input signal 32is the same as the output signal 34 as long as the polarity, eitherpositive or negative, of the pole voltage applied to both the inputtransducer 12 and output transducer 14 is the same.

Conversely, as shown in FIG. 3C, when the polarity of the pole voltageapplied by the DC switching voltage source to the output transducer 14is the opposite from the polarity of the fixed voltage pole source 24,the output signal 36 is shifted 180 degrees out of phase from the inputsignal 34. Consequently, since the output from the DC switched voltagesource 28 switches between positive polarity and negative polarity inunison with a digital or binary data signal, the output signal 32 (FIG.3A) or 36 (FIG. 3C) is phase encoded with the binary or digitalinformation. The data may be subsequently extracted by phasedemodulation at the central station (not shown).

Although FIG. 1 illustrates the fixed pole voltage source 24 asconnected to the input transistor 12 and the DC switched pole voltagesource 28 connected to the output transistor 14, the voltage sources 24and 28 may be switched without affecting the operation of the modulator10. Likewise, although the fixed pole voltage source 24 has beendescribed as a positive voltage source, it may alternatively have anegative polarity without affecting the operation of the modulator 10.

With reference now to FIG. 2, the entire modulator, except for the radiofrequency source 16 and pole voltage sources 24 and 28, is preferablyimplemented as an integrated circuit. As shown in FIG. 2, thepiezoelectric transducers 12 and 14 together with their associated DCblocking capacitors 20 and 22 are connected in series between toterminals 17 and 19. These terminals 17 and 19 are adapted forconnection with the radio frequency signal source 16 and an appropriateoutput 18, such as an antenna. Similarly, a terminal 25 is adapted forconnection with the fixed DC voltage pole source 24 through the resistor26 to bias the first transducer 12. Similarly, a terminal 29 is adaptedfor connection with the DC binary switched pole voltage source 28 tobias the output transistor 14 through a resistor 30.

From the foregoing, it can be seen that the present invention provides abinary bi-phase shift modulator to modulate a radio signal by phasemodulation which consumes extremely little power. Having described ourinvention, however, many modifications thereto will become, apparent tothose skilled in the art to which it pertains without deviation from thespirit of the invention as defined by the scope of the appended claims.

The invention claimed is:
 1. A binary bi-phase shift modulatorcomprising: an input piezoelectric transducer and an outputpiezoelectric transducer connected in series between a radio frequencyinput and radio frequency output, a DC pole voltage source connected toone of said transducers configured to apply a pole voltage of a firstpolarity, a DC switched pole voltage source connected to the othertransducer configured to apply a pole voltage which switches betweensaid pole voltage of said first polarity and a pole voltage of theopposite polarity in accordance with a binary data signal so that thephase of the radio frequency input relative to the radio frequencyoutput varies as a function of the polarity of the DC switched polevoltage.
 2. The modulator as defined in claim 1 wherein said inputtransducer is a lead zirconate titanate transducer.
 3. The modulator asdefined in claim 1 wherein said output transducer is a lead zirconatetitanate transducer.
 4. The modulator as defined in claim 1 andcomprising a first DC blocking capacitor connected in series between theradio frequency input and said input transducer.
 5. The modulator asdefined in claim 4 and comprising a second DC blocking capacitorconnected in series between the radio frequency output and said outputtransducer.
 6. The modulator as defined in claim 5 wherein saidtransducers and said capacitors are implemented as an integratedcircuit.
 7. A method for modulating a radio frequency signal comprising:connecting an input piezoelectric transducer and an output piezoelectrictransducer in series between a modulator input and a modulator output,supplying a radio frequency signal to said modulator input, applying apole voltage of a first polarity to one of said transducers, phasemodulating said modulator output relative to said modulator input byapplying a pole voltage on the other transducer that switches betweensaid pole voltage of said first polarity and a pole voltage of theopposite polarity in accordance with a binary data signal.
 8. The methodas defined in claim 7 wherein said input transducer is a lead zirconatetitanate transducer.
 9. The method as defined in claim 7 wherein saidoutput transducer is a lead zirconate titanate transducer.
 10. Themodulator as defined in claim 1 wherein the DC pole voltage sourceapplies a fixed DC voltage of the first polarity.
 11. The modulator asdefined in claim 1 wherein the resonant frequencies of the inputpiezoelectric transducer and the output piezoelectric transducer arematched to the frequency of the radio frequency of a signal which ismodulated.
 12. The modular as defined in claim 1 wherein the modularoutput is shifted 180 degrees out of phase from the modulator input. 13.The modulator as defined in claim 5 further comprising: a first resistorconnected between the DC pole voltage source and the one transducer, anda second resistor connected between the DC switched pole voltage sourceand the other transducer, wherein an end of the first resistor connectsto the connection between the first DC blocking capacitor and the onetransducer, and an end of the second resistor connects to the connectionbetween the other transducer and the second DC blocking capacitor. 14.The modulator as defined in claim 1 further comprising: a first terminaladapted to connect the DC pole voltage source to the one transducer, anda second terminal adapted to connect the DC switched pole voltage sourceto the other transducer.
 15. The method as defined in claim 7 whereinthe pole voltage of the first polarity is a fixed DC voltage.
 16. Themethod as defined in claim 7 wherein the resonant frequencies of theinput piezoelectric transducer and the output piezoelectric transducerare matched to the frequency of the radio frequency of a signal which ismodulated.
 17. The method as defined in claim 7 wherein the modularoutput is shifted 180 degrees out of phase from the modulator input. 18.The method as defined in claim 7 wherein the radio frequency signal is asinusoidal signal.
 19. The method as defined in claim 18 wherein theradio frequency signal has a frequency less than 100 MHz.
 20. The methodas defined in claim 7 wherein the pole voltage applied the one of thetransducers is V of either positive or negative voltage, and the polevoltage applied to the other of the transducers switches between +V and−V voltages.